Electronic target scoring methodology

[PaulB]

I am trying to confirm that an electronic target (Megalink) is properly scoring the shots. Once the x-y coordinates of the center of the shot are generated by the sound pressure sensors it should just be a geometry problem. Please see if you find any problem with my logic.

For air rifle the 10 dot is 0.5mm diameter and the 9-ring is 5.5mm. The pellet is 4.5mm (I will use this "nominal" value even though a scoring plug can be as large as 4.55mm). Thus, the widest shot that will score a 10.0 will be ((0.5/2) + (4.5/2)) = 2.5mm, center-to-center distant from the middle of the target (the sum of the two radii).

If the 10 dot is divided into 10 equal rings for decimal scoring the size of these rings is as follows, with the range of c-t-c distances that will produce this score:

score diameter radius c-t-c range
10.0 0.50 0.250 2.25 - 2.500
10.1 0.45 0.225 2.00 - 2.249
10.2 0.40 0.200 1.75 - 1.999
10.3 0.35 0.175 1.50 - 1.749
10.4 0.30 0.150 1.25 - 1.499
10.5 0.25 0.125 1.00 - 1.249
10.6 0.20 0.100 0.75 - 0.999
10.7 0.15 0.075 0.50 - 0.749
10.8 0.10 0.050 0.25 - 0.499
10.9 0.05 0.025 0.00 - 0.249

With the x-y coordinates generated by the device one just has to take the square root of the sum of the squares of the coordinates to get the center to center distance. For example: a 10.0 produced x=1.943, y=1.205;
SQR(1.943^2 + 1.205^2) = 2.2863 (within the range in the table). However, I looked at a number of fired 10.0's and the range of values seemed to be between 2.00 and 2.5, twice as large as my calculated spread.

An examination of nine 10.4's showed four shots between 1.38 and 1.48 (within my calculated range) and five shots of from 1.02 to 1.04 (well below my range). Don't know why I seemed to get the two clusters of values, with nothing in between (maybe just poor statistics from my small number of shots examined).

Am I doing this right?, wrong?, any suggestions?

[Spencer]

e-mail sent

[David Levene]

This sounds like a question from the ISSF EST Judges course I was on a couple of weeks ago.

To score a 10.00 the centre of the pellet must be no more than 2.50mm from the centre of the target (the radius of the ten plus the radius of the pellet). The decimal scoring rings are therefore 0.25mm apart, which gives:-

Up to 0.25 = 10.9
Up to 0.50 = 10.8
Up to 0.75 = 10.7
Up to 1.00 = 10.6
Up to 1.25 = 10.5
Up to 1.50 = 10.4
Up to 1.75 = 10.3
Up to 2.00 = 10.2
Up to 2.25 = 10.1
Up to 2.50 = 10.0

Your method of calculating the distance from the x and y coordinates is correct.

edit note: The above should obviously read "Up to and including....."

[PaulB]

Thanks Spencer and David. You have verified my methodology. Now all I have to do is confirm correct operation of the system that I am analyzing.

[David Levene]

Now all I have to do is confirm correct operation of the system that I am analyzing.

Any likely problems would result in incorrect measurement of the x and y coordinates. Once they have been ascertained the rest is just mathematics.

If you have a log print showing x and y coordinates that give different results from those reported by the system then you might want to ask Megalink for an explanation.

I will also send you a PM.

[Tim Conrad]

If you can, please post a printout or link to the output from the target in question. Megalink has received ISSF approval for their 10 meter system, as well as 50 meter. I assume (dangerous) that the scoring accuracy would have been verified. In my experience (Megalink user and tech support for North America) the shots are scored properly. If you have something to the contrary, we should examine it.

[David Levene]

Any update on this problem Paul?

[pilkguns]

This is a good thread to ask a question of mine that I would like to know.

What value does the electronic scorer assign to the diameter of a the hole? A nominal 4.50 I assume, but don’t know for a fact but really there is no way that this can be consistently scored.

The ten dot is .5mm . That is exact enough. Pellets come from 4.48 mm head size (which cuts the hole) to 4.52 mm also exact. On a paper target a 10.0 score has to just barely touch the white dot. Assuming one competitor is usinng 4.48 pellets and another is using 4.52 pellets, and both guns shoot equally accurate (i.e. the barrel fit for each is the maximum for accuracy) the first competitor has to shoot .4mm closer to the center to achieve the same score. Pretty significant considering the 10 dot is only .1 mm larger.

Am I missing something? If I am not, then is this part of the reason why better scores are being shot today, simply because all score are now gauged as 4.50 wide, when before we had to rely on visual cut holes up to the white dot.

Because here is the interesting thing. I have measured a lot of pellets in the last few years, trying to determine what makes accuracy. I have seen pellets from major manufacturers of target pellets, with head sizes as low as 4.46, despite what they were marked on the tin. This would be due to the lead shrinking as part of its aging process I assume. But in that case, think how far that is from the 10 score.

[David Levene]

Assuming one competitor is usinng 4.48 pellets and another is using 4.52 pellets, and both guns shoot equally accurate (i.e. the barrel fit for each is the maximum for accuracy) the first competitor has to shoot .4mm closer to the center to achieve the same score. Pretty significant considering the 10 dot is only .1 mm larger.

The difference is actually 0.04mm Scott, and that's diameter so the edge of the hole would be 0.02mm closer to the line.

You should also remember that, for air rifle, paper targets have +/-0.1mm on ring diameter. You also have +0.00mm/-0.05mm tolerance on the outward scoring gauge.

Electronic scoring targets work on an exact ring size and consistent 4.50mm hole diameter. I'm not sure about the other manufacturers but Sius Ascor 10m targets have a theoretical accuracy of 0.05mm and a practical accuracy of 0.1mm.

[pilkguns]

obviously I did'nt have enough coffee intake doing that math this morning.

[Tim Conrad]

The small dot in the middle (air and USA-50) is not really used. The rules call for outward scoring, with the gauge inside or just touching the 8 ring. The inner dot is used for scoring inner tens, sometimes. All acoustic electronic targets base their score on the center of impact, not the edge of the pellet. When you specify a target, the system also knows the projectile size, 4.5 or 5.6 mm. That is only used in impact point calculations, as the sound arrives at the microphones slightly earlier with larget bullets or pellets. Variations in pellet size are below the resolution of the system.

As noted by others, the practical limit is around 0.1mm. Some folks claim better, but based on speed of sound, and rise time in the microphones, it doesn't get better than 0.1 A tenth of a ring is around 0.25mm. While the scoring plug has better tolerances, paper printing accuracy is worse than that. So e-targets should be at least as good as the best paper.

[David Levene]

The inner dot is used for scoring inner tens, sometimes.

Presuming that we are talking about the ISSF Air Rifle target (or US equivalent) then you shoudn't actually be using the inner dot for gauging at all.

ISSF rule 6.3.2.8.4.1 makes it clear that you should be using an Air Pistol outward scoring gauge to score Air Rifle inner tens. The actual method is quoted as:-

"If the measuring edge of an Air Pistol Outward scoring gauge does not go outside the 7 ring of an air rifle target then the shot value is an inner ten."

[Tim Conrad]

Gary Anderson told is that at the ISSF B class a few weeks back. However, using the Air Pistol outward gauge inside the 7 ring requires a 10.4 for an i.t., whereas the old rule, inward gauge covering the dot, only needs a 10.3 At least it treats everyone the same.

The USA-50 target has similar problems. I don't think USAS has released the new rulebook, so officially we break ties on 10 shot strings, except at matches where we don't, like air pistol at the Winter Air Gun match. With american paper targets, i.t.'s are a pain to score in smallbore.

Makes it harder for e-targets, as they work only on distance from center. As far as I know, Megalink is still on the old rule, 10.3 for i.t.

[Sawyer]

Scott, would one not have to ignore the variation in pellet (skirt) size and instead measure bore diameter? I'm assuming all pellets will form to the bore, so the actual size of the pellet would only be material to accuracy, not the size of the hole punched. Tim is correct in how the scoring is done. But to answer your question, here's my theory:

Assuming the same accuracy between two guns, you could theoretically achieve a higher score on paper targets with the gun that has the larger bore. The skirt will expand to the bore diameter and thus "trim out" the hole after it is initially cut by the head of the pellet. This would be a benefit when using a plug to measure a hole on a paper target, but of no benefit on electronics, where the system measures only the center, not the outside (which is what we're really looking at when using outward scoring guages).

Hopefully I made some sense here. It's all theorizing but fun nevertheless.

[j-team]

The skirt will expand to the bore diameter and thus "trim out" the hole after it is initially cut by the head of the pellet.

Hopefully I made some sense here. It's all theorizing but fun nevertheless.

After firing the head and the skirt will both be the same size as the bore. Catch a fired pellet, there's rifling mark head and skirt. If the skirt is bigger, that would mean that the head hasn't touched the bore. If that were the case I doubt that there would be much accuracy to worry about!

All the talk about pellet diameters effecting score would only be case if close shots are scored visually, without a gauge. If done with a plug gauge then that's the diameter (even more irrelevant as they are outward gauges!), if by electronics then they determine the diameter.

[David Levene]

Gary Anderson told is that at the ISSF B class a few weeks back. However, using the Air Pistol outward gauge inside the 7 ring requires a 10.4 for an i.t., whereas the old rule, inward gauge covering the dot, only needs a 10.3 At least it treats everyone the same.

I'm sorry but for at least the last 17 years a 10.2 on an ISSF Air Rifle target has been an inner 10, and it still is. Nothing has changed.

An Air Pistol outward gauge not going outside the 7 ring on an Air Rifle target scores 10.2, which is an inner 10. (Remember that it's the outside edge of the 7 ring).

The decimal scoring rings on an Air Rifle target are 0.25mm apart (0.5mm diameter).

For a 4.50mm diameter hole to completely remove the 0.5mm diameter 10 dot on an AR target the centre of the hole must be 2mm from the centre of the target.

As I said, nothing has changed in the ISSF's interpretation of an Air Rifle inner 10 in at least 17 years, only the way that it is measured.

As far as I know, Megalink is still on the old rule, 10.3 for i.t.

I hope not. As above, it has always been 10.2.

[Tim Conrad]

My bad, thinking of another target. Air rifle looks OK, no change.

[Guest]

The skirt will expand to the bore diameter and thus "trim out" the hole after it is initially cut by the head of the pellet.

Hopefully I made some sense here. It's all theorizing but fun nevertheless.

After firing the head and the skirt will both be the same size as the bore. Catch a fired pellet, there's rifling mark head and skirt. If the skirt is bigger, that would mean that the head hasn't touched the bore. If that were the case I doubt that there would be much accuracy to worry about!
.

Never looked at one that closely but that certainly makes sense. But does the skirt not engage the rifling more deeply than the head? More surface area?

[Tim Conrad]

The rifling is extremely fine, so there would be little size change from head to skirt. The paper is another matter. On good paper, Edelmann or Kruger, the grain of the paper will extend inward from the hole. You can lift a pellet by the skirt. On US paper, the holes are not so clean. In either case, the plug should center in the hole, so diameter of the hole is not really an issue. And any shot close to the center dot should be plugged as a matter of course. I generally look at the outside edge of the hole. If it touches the white part of the 8-ring, it will plug out. If the hole takes a bite out of the center dot, it will plug in. Between those extremes, plug it.

[David Levene]

My bad, thinking of another target.

Out of interest, which one. I didn't think that any ISSF targets had changed so would like to know if I missed one.